MicroRNA (miRNA) is an RNA of 16 to 28 nucleotides that is not translated into a protein, and it is currently known that 2590 miRNAs are present in human according to the miRBase release 21 (http://www.mirbase.org/). In recent years, miRNAs have been receiving attention as molecules for suppressing in vivo expression of various genes. On the genome, a region of each of miRNA gene is present and is transcribed into a RNA precursor with hairpin loop by RNA polymerase II, and the RNA precursor is then cleaved by two types of dsRNA cleaving enzymes having RNase III cleavage activities that are called Drosha in the nucleus and Dicer in the cytoplasm, thereby forming a mature miRNA. It is known that the mature miRNA is taken into the protein complex called RISC and interacts with mRNAs of a plurality of target genes having complementary sequences to suppress the expression of a gene (Non Patent Literature 1).
Certain types of miRNAs are suggested to be associated with human diseases including cancer, and particularly in cancer, for examples, many miRNAs such as hsa-miR-4450, hsa-miR-6893-5p and hsa-miR-575 are known to be markers specific to pancreatic cancer in blood (Non Patent Literature 1 and Patent Literature 1).
Further, in addition to the miRNAs associated with the growth of cancer cells, the presence of a miRNA which works in a direction of suppressing cancer cells is reported, suggesting a method for treating cancer utilizing the expression pattern of the miRNA. Specific examples of the known method include a method for treating diseases such as cancer by administering an activated serum comprising 153 miRNAs such as hsa-Let-7a and upregulating the miRNA (Patent Literature 2), a method for treating lung cancer using a body fluid comprising many miRNAs such as hsa-Let-7a (Patent Literature 3), and a method for treating blood cancer by administering antisense oligonucleotides of many miRNAs such as miR-1321 comprised in circulating exosomes in the body (Patent Literature 4).